Vehicle fuel tanks are typically filled by way of a one-way fuel inlet admitting fuel under pressure from a pump. As the tank is filled and the fuel level rises, a volume of air and fuel vapor must be removed from the tank to enable the fuel to be pumped into the tank up to the controlled "full" point.
When the vehicle has been in a high engine load condition for a significant time period, the fuel in the tank becomes hot due to the heat that is introduced by the return of surplus fuel from the hot engine and heat input from the vehicle underbody. The high temperature fuel can generate a high vapor pressure condition in the tank and will rapidly evaporate when the fuel cap is removed. To prevent spraying of fuel when the filler cap is removed, and to permit the effective filling of the tank, the vapor in the tank must be removed by way of a valve.
The valve must handle the high vapor and air flow without premature closing.
The venting system thus far described is operative only when the fuel cap is removed. Another venting valve not described in detail herein is used to enable a controlled venting of the fuel tank when the fuel cap is on the vehicle. One preferred venting valve for this purpose is shown in U.S. Pat. No. 4,753,262 assigned to the assignee of this application.